This invention relates in general to bearings and, more particularly, to a bearing assembly which monitors forces and torques transmitted through it to provide electrical signals for use by devices which monitor and control vehicular dynamics based upon calculated tire patch loading or to determine the general stresses, strains, and loads placed upon a bearing.
There are a number of applications where the loads and types of loads placed on a bearing in operation can provide significant information about the bearing and the objects attached to the bearing. One such application is in the automotive industry where such loading information, in electrical signal form, is vital for the proper application of Vehicular Dynamic Control (“VDC”) systems. Another application is in the steel rolling mill industry where electronic processing and control is used to manipulate the speed and torque of rollers during the rolling process. Yet another application is the machine tool industry where programmable controllers and processors monitor and control the speed of spindles in milling, cutting, and drilling machines.
In the automotive industry, many vehicles of current manufacture come equipped with antilock braking systems. A system of this type monitors the rotation of the wheels on a vehicle and, when the brakes of the vehicle are applied, relaxes the breaking force at any wheel which locks up and skids. This reduces the tendency of the vehicle to veer off course when the traction at the wheels differs and makes the vehicle easier to steer under such circumstances. A few vehicles have traction control systems. This type of system monitors the rotation of driven wheels and distributes the tractive effort between those wheels, so that one does not break loose and spin. While both systems enable the driver of a vehicle to maintain better control over the vehicle, other factors influence the operation of the vehicle and, notwithstanding the successful operation of an antilock braking system and a traction control system, those other factors may still cause a vehicle to go out of control.
Significant among those other factors are the centrifugal forces encountered by a vehicle when it negotiates a turn—forces which act laterally on the vehicle. The friction between the vehicle tires and the road surface, that is at the so-called “tire contact patches”, resists these forces, but sometimes the friction may not be enough and the vehicle will slide, and perhaps go out of control, particularly if operated by one having poor driving skills. Then again, the frictional forces at the tire contact patches may prevent sliding, but the centrifugal force generated by the turn, inasmuch as it acts at the center of gravity, which is above the tire contact patches, may be sufficient to topple the vehicle.
Automobile manufactures have turned to VDC systems to prevent automobiles from going out of control in turns. The typical VDC system relies on a yaw sensor which measures the rate of change in yaw (rotation of the vehicle about its vertical axis) and a lateral acceleration sensor to, in effect, measure the centrifugal force imposed on the vehicle as a consequence of negotiating the turn. A VDC system also takes into account the angular velocity of the road wheels, the position of the steering wheel, and the power delivered by the engine. The typical VDC system analyzes the information and modulates the operation of the engine, as well as the brakes, to better maintain control of the vehicle in the turn.
The more sophisticated VDC systems also factor into the real time analysis estimated loads at the individual wheels and thus seek to evaluate conditions at the tire contact patches. But when negotiating a turn, each tire contact patch experiences forces and torques that do not comport with simle analytical procedures. Thus, measuring the displacement of a shock absorber piston, for example, does not give a very reliable indication of conditions that exist at the tire contact patch below that shock absorber. Certainly, it provides no indication of the torque at the tire contact patch, much less of the location at which the resultant of the force at the tire contact patch is acting.
Bearing assemblies exist which incorporate the use of strain gages to provide certain information regarding various bearing loads. For example, an antifriction rolling bearing disclosed in U.S. Pat. No. 5,140,849 issued Aug. 25, 1992, uses two strain gages to monitor the general loads applied to a bearing. This bearing, however, is unable to provided the multi-faceted data needed by high level VDC electronic systems or by the processor controlled systems in the rolling mills industry or the machine tool industry.
U.S. Pat. No. 4,748,844 discloses a load detection device more related to the automotive industry. That device consists of a multi-component load cell structure fixed to a hub on which a road wheel is mounted, the load cell structure being attached so as to rotate with the tire of the wheel. While that device provides some signal benefits, this device cannot provide signals indicating all loads and all torques required to enable a high level VDC electronic device to function properly. In particular, that device mounts all of its strain gages in only one plane which is perpendicular to the axis about which the wheel rotates. As a result, the signals from the strain gages on that device are unable to detect the forces tending to cause a vehicle to skid sideways or to roll the vehicle over.
Therefore, while the automotive industry is continuing to develop electronic devices which assist the driver to maintain control of his vehicle through various combinations of brake application and continuous suspension adjustment, the more sophisticated of these systems require reliable input signals indicating the full spectrum of loading which are indicative of the loads exerted at the tire contact patch.
Similarly, the rolling mill and machine tool industry utilize various forms of process controls which require monitoring of the loads placed on bearings. Specifically, rolling mills need bearing feedback regarding indications of belt slipping on rollers or indications that a particular set of rollers is experiencing higher loads and torques. Computer controlled machine tools need to monitor the amount of torque being experienced by a bearing supporting a spindle in order to assess whether cutting and drilling tools have becomes dull or whether the cutting or drilling speeds exceed the limits established for proper machining operations.